1. Field of the Invention
The present invention relates to a scanning device used in products such as facsimile machines, scanners, and multi-function printers (MFP), and relates more particularly to a duplex scanning device for scanning both sides of an original document.
2. Description of the Related Art
Duplex scanners according to the prior art for scanning both sides of a document have either had a mechanism for reversing the original document or two sensors for scanning the opposite sides of the document.
However, the entire transportation path cannot be formed in a straight line in scanners having a reversing mechanism, and jams occur easily when transporting thin documents and thick documents. Furthermore, the curvature of the transportation path tends to cause thick originals to curl. This curl can also cause the original document to lift away from the sensor surface, and thus tends to degrade scanned image quality. Furthermore, adding the transportation path needed to reverse the original document necessarily increases the overall size of the product.
A problem with duplex scanners having two scanning sensors is that the duplication of parts results in a more complicated construction and a higher cost.
To therefore resolve these problems Japanese Patent Laid-Open Publication (kokai) H5-336305, for example, teaches a device that scans both sides of an original document using a single sensor by rotating and positioning the sensor unit containing the image sensor according to whether the front or back side of the document is being scanned.
With the prior art method described above, however, a large space is needed to rotate the image sensor and platen roller because of the large radius of rotation required by the image sensor and platen roller, and this increases the size of the product.
Furthermore, because a straight transportation path cannot be formed with the above-described prior art, paper jams occur easily during transportation, the paper lifts away from the sensor surface, and scanning quality is easily degraded.